Traction vehicle for aircraft and engagement and hoisting device therefor

ABSTRACT

A traction vehicle for moving a nose wheel of an aircraft comprises a wheel-mounted chassis including an engagement and hoisting device that can be raised and lowered. The engagement and hoisting device has a nose-wheel holder and a U-shaped stand having an opening facing the aircraft. The nose-wheel holder and the stand are shaped as two separate units and have co-operating journaling members arranged in a circular arc to provide rotational movement between the holder and the stand.

BACKGROUND OF THE INVENTION

The present invention relates to a traction vehicle for ground movementof an aircraft, having at least one nose wheel, which traction vehiclecomprises

a wheel-mounted chassis and

an engagement and hoisting device that can be raised and loweredrelative to the chassis and is of a type that is brought into freelycarrying engagement with the nose wheel and which comprises

a stand, being substantially U-shaped with its opening turned towardsthe aircraft,

journalling members, flexibly connecting the stand to the chassis,

actuators, arranged between the stand and the chassis to raise and lowerthe engagement and hoisting device relative to the chassis, and

a nose-wheel holder, having

an inner space that can be opened in the direction of the nose wheel forreceiving the same,

carrying members for carrying the nose wheel in said space, and

forward and rear wheel supports for holding the nose wheel in thelongitudinal direction of the traction vehicle.

The invention also relates to such an engagement and hoisting device.

Once the maximum steering angle of an aircraft has been attained, whilstmoving the aircraft on the ground with the aid of a traction vehiclecoupled to the nose wheel of the aircraft, when the direction of travelof the traction vehicle is changed, torque is transferred to thenose-wheel stand via the nose wheels and its upwardly-directed steeringor rotary axle. This torque must not exceed prescribed values laid downby the various aircraft manufacturers in question. In the following,this maximum permitted torque is referred to as the maximum torque ormaximum value.

A traction vehicle in accordance with the preamble to claim 1 is knownthrough SE-500 744. The engagement and hoisting device supported by thechassis of the traction vehicle is arranged to be brought into astarting position close to, but not touching, the nose wheels of theaircraft, both in front of and behind the contact point between the nosewheels and the ground, when the traction vehicle is moved relative tothe nose wheels, and to be raised from said starting position in order,when in free surface contact with the nose-wheel tread on both sides ofsaid contact point with the ground, to be brought into releasableengagement with the nose wheels so that the same are lifted from theground when the engagement and hoisting device is raised. The engagementand hoisting device forms a rigid connection between the nose wheels andthe chassis. Thus, to enable a change of angle between the tractionvehicle and the aircraft, the steering hydraulics of the aircraft mustbe disconnected and the rotary movement of the nose wheels limited bymechanical terminal stops on the aircraft. At these terminal stops, theaircraft has attained its maximum steering angle and torque will betransmitted to the nose-wheel unit, via the rotary axle of the nosewheels, wherein, as mentioned above, the torque value must not exceed amaximum value determined by the manufacturers of the aircraft. Exceedingthe maximum torque without forewarning presents a very great risk of thenose-wheel unit being damaged. SE-501 788 describes a device formeasuring and indicating the steering angle of the aircraft relative tothe traction vehicle in order, thereby, to prevent the nose-wheel standbeing subjected to the harmful maximum torque. However, such a devicehas the disadvantage that, for instance, a sensor wire must be connectedto the aircraft. As designs differ from one aircraft to another, it canbe difficult to provide equipment to suit all the types of aircraft atraction vehicle must be able to handle.

In another type of traction vehicle, the same is connected to theaircraft with the aid of a traction rod, where torque is limited withthe aid of a breakpin in the traction rod or in the fastening of thetraction beam to the nose-wheel stand. A disadvantage with this systemis that no forewarning is provided before the pre-set torque is exceededso that the traction vehicle must be substituted or the traction rodreplaced. In addition, there is a risk of the nose-wheel stand beingdamaged because the traction rod is released from the aircraft in somecases.

U.S. Pat. No. 4,576,245 describes a tractor for towing a helicopter ormedium-sized aircraft. The tractor has an engagement and hoisting devicethat can be raised and lowered and consists of a wheel-borne chassis,formed by two beams and a platform mounted thereon, and also a supportplate, pivotably journalled on the platform by means of a thrust bearingand intended to support the nose wheel. The support plate has an uprightwith a hydraulic cylinder, the piston rod of which is provided with ayoke with screws for securing the piston rod to the nose wheel. Thehelicopter is drawn towards the tractor with the aid of the hydrauliccylinder so that the nose wheel rolls onto the lowered platform to bereceived on the support plate and retained thereon with the aid of thehydraulic cylinder. Thereafter, the chassis is raised to its towingposition. WO 98/25822 describes a tractor for towing an aircraft. Thetractor has a platform for carrying the nose wheel. The aircraft ismoved forwards towards the platform, whereupon the nose wheel is movedonto the platform with the aid of a ramp. The platform can be providedwith a rotary plate on which the nose wheel rests. However, the WOspecification does not show any device for retaining the nose wheel onthe rotary plate and platform. The platform is arranged such that it canperform a swinging or pendulum movement relative to the chassis in thelongitudinal direction of the tractor from a resting position. When theaircraft is moved on the ground, the deviation of the swinging orpendulum movement from the resting position is a measure of the load onthe nose wheel in the horizontal and vertical direction. By measuringthe swinging or pendulum movement with a linear-movement or angletransducer, the load can be kept within prescribed values by limitingthe acceleration or retardation of the tractor when too great adeviation from the resting position is measured. The known tractionvehicles in accordance with U.S. Pat. No. 4,576,245 and the WOspecification 98/25822 are of a type completely different from the oneto which the invention refers. Unlike the traction vehicle in accordancewith the invention, they cannot be used for aircraft of varying sizesand they are not intended to be docked to the aircraft. They lack, andcannot be provided with, an engagement and hoisting device that can beraised and lowered relative to a chassis and has a U-shaped stand toenable said docking to a stationary aircraft and provide freelysupporting engagement with the nose wheel with the aid of a specialnose-wheel holder, the engagement and hoisting device being raised tolift the nose wheel from the ground.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a traction vehiclewith an improved engagement and hoisting device that enables securitydemands from aviation authorities or operative or functional demandsfrom users to be met so that an improved control of and security duringthe ground movement of the aircraft is obtained, as compared with knowntraction vehicles.

The traction vehicle, as well as the engagement and hoisting device, ischaracterised in

that the nose-wheel holder and the stand are shaped as two separateunits and comprise co-operating journalling members, arranged in acircular arc and defining a vertical axis of rotation for said units and

that the nose-wheel holder is substantially U-shaped with its openingturned towards the aircraft as viewed in a starting position, when thenose-wheel holder is situated to be moved into a position to receive thenose wheel.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further described in the following with referenceto the drawings.

FIG. 1 shows a traction vehicle with an engagement and hoisting devicein accordance with the invention carrying an aircraft by its nose wheel.

FIG. 2 shows the engagement and hoisting device in accordance with FIG.1 with its nose-wheel holder rotated in one direction relative to itsstand.

FIG. 3 shows the engagement and hoisting device in accordance with FIG.2, but with the nose-wheel holder rotated in the other directionrelative to its stand.

FIG. 4 shows the journalling of the nose-wheel holder to the stand.

FIG. 5 shows an engagement and hoisting device similar to the one inFIG. 2, but additionally provided with a break-device between thenose-wheel holder and the stand, the engagement and hoisting devicebeing open and ready to receive the nose wheels.

FIG. 6 shows the engagement and hoisting device in accordance with FIG.5 engaged with the nose wheels.

FIG. 7 shows an engagement and hoisting device similar to the one inFIG. 2, but additionally provided with a braking mechanism between thenose-wheel holder and the stand.

FIG. 8 shows the braking mechanism in FIG. 7.

FIG. 9 shows an engagement and hoisting device similar to the one inFIG. 2, but additionally provided with a torque indicator between thenose-wheel holder and the stand.

FIG. 10 shows the torque indicator in FIG. 9.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an aircraft 1 and a traction vehicle 2, provided withwheels, for moving the aircraft 1 relatively short distances on theground. The aircraft 1 has a nose-wheel unit 3, comprising two nosewheels 4 and an upwardly-directed steering or rotary axle 5 that carriesthe nose wheels 4 and is rotatably journalled to the nose-wheel unit 3and lockable in the same with a hydraulic locking mechanism (not shown)to lock the single wheel axle 6 of the nose wheels 4 in a position atright angles to the longitudinal direction of the aircraft 1. Thetraction vehicle 2 comprises a chassis 7, carrying, at one of its endportions, a driver's cabin 8 and including two longitudinal, horizontalbeams 9, 10, spaced a pre-determined distance from each other to definebetween them a space 11, which is open at the end that faces away fromthe driver's cabin 8 to be positioned in accordance with the aircraft 1,when the aircraft 1 is to be moved on the ground. At their free endportions, which are turned towards the aircraft 1, the two beams 9, 10each have a wheel or pair of wheels (not visible in FIG. 1).

The traction vehicle 2 comprises an engagement and hoisting device 12that can be raised and lowered to be brought into freely supportingengagement with the nose wheels 4, this being the only engagementlocation, which thus means that the remainder of the traction vehicle 2is completely free from contact or engagement with the nose-wheel stand3, and to lift the nose wheels 4 from the ground sufficiently to enable,the aircraft 1 to be moved with the aid of the traction vehicle 2. Theengagement and hoisting device 12 is located in said space 11 betweenthe beams 9, 10 and carried by the same via actuators 13 in the shape ofpower cylinders, by means of which the engagement and hoisting device 12can be lowered to a lower position at ground level and raised to atowing position, in which the engagement and hoisting device 12 is clearof the ground, as are the nose wheels 4. Further, the engagement andhoisting device 12 is flexibly connected to the chassis 7 viajournalling member 15 with suitable elements at its ends to allow theengagement and hoisting device 12 to change positions as desired. In theembodiment shown, the journalling member 15 is formed by four link armsarranged in pairs. Alternatively, it can consist of a single link arm.

As further illustrated in FIG. 2, for instance, the engagement andhoisting device 12 comprises a stand 17 and a nose-wheel holder 18,designed as two separate units and rotatably journalled relative to eachother. The stand 17 and the nose-wheel holder 18 are both substantiallyU-shaped.

The U-shaped stand 17 is arranged horizontally and comprises tworearwardly-turned legs 19, 20 and a transverse connection piece 21,which rigidly connects the legs 19, 20 to each other and extends atright angles to the longitudinal direction of the traction vehicle 2 andon which said link arms 15 are journalled on its outside. The legs 19,20 and connection piece 21 comprise internal, horizontal bottom plates22, seamlessly merging into each other and having arc-shaped inner edgeportions 23 so that the stand 17 obtains a vertical inside 24 with apre-determined radius.

The U-shaped nose-wheel holder 18 is horizontally arranged within theU-shaped stand 17, in the same plane, and comprises two legs 30, 31 anda connection piece 32, rigidly connecting the legs 30, 31 to each otherand facing the inner parts of the stand 17 (including the connectionpiece 21 of the stand 17). Each leg 30, 31 has a vertical wall 33, 34 onits inside, the two walls 33, 34 being parallel with each other anddefining between them an inner nose-wheel space 35, adapted to the widthof the nose wheels 4 so that the same can be received therein withsufficient play against the legs 33, 34, the width of the space 35 beingsufficiently large so that even the nose wheels of large aircraft can bereceived therein, i.e. a single traction vehicle can in principle beused for aircraft of all sizes.

The nose-wheel holder 18 has outer edge portions 36 that are arc-shapedso that it obtains a vertical outside 37 with a pre-determined radiussomewhat greater than said radius of the inside 24 of the stand 17.

The stand 17 and the nose-wheel holder 18 are designed as two separateunits, as mentioned above, and comprise co-operating journalling members70, 71, arranged in a circular arc corresponding to the length of thecurved insides 24 and outsides 37 to create a rotation girdle. Theseouter journalling members 70, 71 define a vertical axis of rotation forsaid units 17, 18. The journalling member 70 of the stand 17 comprises aplurality of rolling elements, equidistantly mounted on the topside ofsaid bottom plates 22 with the aid of angle profiles 25 along a circulararc of a pre-determined radius. As further illustrated in FIG. 4, eachangle profile 25 carries a first roller 26, journalled on a verticalshaft journal 27 on the horizontal part of the angle profile 25, and asecond roller 28, journalled on a horizontal shaft 29 on the verticalpart of the angle profile 25. Adjacent to the outside 37 of thenose-wheel holder 18, that is radially inside the same, the outer edgeportion 36 of the nose-wheel holder 18 is provided with a horizontalcarrying and rolling surface 38 for co-operation with the second rollers28 of the rolling elements and with two vertical, inner and outer,concentric, supporting and rolling surfaces 39, 40 for co-operating withthe first rollers 26 of the rolling elements. Thus, said carrying androlling surface 38 and supporting and rolling surfaces 39, 40 togetherform the journalling members 71 of the nose-wheel holder 18. Thenose-wheel holder 18 is thus carried by said second rollers 28 via itshorizontal carrying and rolling surface 38, which extends in acontinuous circular arc along the entire outside 37, the carrying androlling surface 38 being located such, relative to the horizontalunderside 41 of the nose-wheel holder 18, that a small clearance gap 42is created between said underside 41 and the horizontal parts of theangle profiles 25, thereby preventing friction between them. The twoconcentric supporting and rolling surfaces 39, 40 and the second rollers28 are arranged at a radial distance from each other that is equal to oronly somewhat greater than the diameter of the second rollers 28. Thetwo supporting and rolling surfaces 39, 40 and the second rollers 28co-operate with each other so that the nose-wheel holder 18 is fixed inthe radial direction irrespective of its rotational position.Consequently, the two supporting and rolling surfaces 39, 40 define thevertical axis of rotation.

Further, the nose-wheel holder 18 comprises an inner carrying plate 43,see FIG. 5, and an inner, horizontal wheel support 44, located apre-determined distance above the carrying plate 43. The carrying plate43 extends between the vertical leg walls 33, 34 and are movably mountedthereon to be displaced relative to the connection piece 21, with theaid of power cylinders (not shown), so that its position can be adjustedand adapted to the dimension of the nose wheel. Thereby, the nose-wheelholder 18 can, with best fit, secure nose wheels of the variousdimensions presented by different types of aircraft. The carrying plate43 has a concave topside that is crudely adapted to the radii ofdifferent nose wheels 4 and can be made in sections, as shown in thedrawings, or uniformly curved. The carrying plate has a lower,horizontal edge portion 45, which has a downwardly sloping surface andis located in level with or slightly below the underside of the stand.The wheel support 44 is pivotably mounted on the nose-wheel holder 18,two power cylinders 46 being flexibly connected, via their piston rods,to the ends of the wheel support 44 to bring the wheel support 44 tobear against the nose wheels 4.

Moreover, the nose-wheel holder 18 comprises an outer carrying plate 48,and an outer horizontal wheel support 49, located a pre-determineddistance above the carrying plate 48 and preferably level with the innerwheel support 44. The carrying plate 48 has a horizontal edge portion50, which has a downwardly sloping surface and is located in level withthe edge portion 45 of the inner carrying plate 43. The outer carryingplate 48 and the outer wheel support 49 together form a gate that ispivotably journalled by means of a vertical rotary shaft, forming partof an actuator 51, in turn rigidly mounted on one of the legs 31 of thenose-wheel holder 18. The gate can be opened and shut with the aid ofthe actuator 51. The outer wheel support 49, which consists of twoparts, is pivotably mounted on the carrying plate 48 via a plurality oflink arms 52. Two power cylinders 53, 54 are flexibly connected, viatheir piston rods, to the ends of the wheel support 49 to bring thewheel support 49 to press against the nose wheels 4, see FIG. 2, forinstance. The two co-operating, opposing wheel supports 44, 49 aresuitably located on a level above, for instance immediately above, ahorizontal plane intersecting the central axles of the nose wheels 4.The nose wheels 4 are thereby also locked in the vertical direction.

The stand 17 and the nose-wheel holder 18 are provided with co-operatingstops 55, 56, 57 that limit the rotation of the nose-wheel holder 18 inboth directions. In addition, the stand 17 is provided with two terminalposition transducers 58, 59, located in front of the two stops 55, 56 onthe stand 17, which terminal position transducers 58, 59 sense the stop57 of the nose-wheel holder 18 to indicate the rotational angle on thenose-wheel holder 18 relative to the stand 17 and the traction vehicle 2to be used for various control functions, for instance to control thetractive force of the traction vehicle 2 so that it does not diminishand approach zero unless the direction of the traction vehicle 2 ischanged back. In the embodiment in accordance with FIGS. 1-3, thenose-wheel holder is freely rotationally suspended on the stand 17 viathe rollers 28 of the rolling element. This means that the angle of thetraction vehicle 2 relative to the nose wheels 4 can vary without anysignificant torque being transferred to the nose wheels 4. In thisembodiment, the nose wheels 4 can be locked, but they can also bedisengaged. It should thus be understood that, when the nose wheels 4are disengaged, the turning radius of the traction vehicle 2 relative tothe aircraft 1 can be further increased by making use of the fullrotation angle of the nose-wheel holder 18 as well as the full rotationangle of the disengaged nose wheels 4.

Although the shown journalling members 70, 71 are currently preferred,they can obviously be designed in many other ways, for instance in theshape of a ball-bearing segment or girdle in one of the units andco-operating rolling surfaces for the balls in the other unit.

FIGS. 5 and 6 show an engagement and hoisting device 12, similar to theone in FIGS. 1-3, but additionally provided with a rotation-inhibitingdevice in the shape of a break-device 60, arranged on the stand 17 andthe nose-wheel holder 18 in proximity to its central stop 57, seen inthe starting position of the nose-wheel holder 18, when the axle 6 ofthe nose wheels 4 is at right angles to the longitudinal direction ofthe traction vehicle 2. The break-device 60 comprises a breakpin 61 thatfixes the nose-wheel holder 18 against rotation in said startingposition. The breakpin 61 is constructed such that it breaks when thenose-wheel holder 18 is subjected to a certain, permitted torquerelative to the stand 17. In this embodiment, the nose wheels 4 of theaircraft 1 are disengaged, whereby the rotary axle 5 of the nose-wheelunit 3 is not permitted to transmit a prescribed, maximum torque to afixed construction element of the nose-wheel unit. Thus, said permittedtorque has a value that is less than the value of said prescribed,maximum torque.

In the embodiment in accordance with FIG. 7, a braking mechanism 62, theconstruction of which is further illustrated by FIG. 8, is used insteadof a break-device. In this case, the nose-wheel holder 18 is likewisefixed against rotation in its starting position, but also in all otherpositions between the two terminal stops. The braking mechanism 63 has abraking head 64, bearing against the outside of the nose-wheel holder 18with the spring force of a spring 65, which spring force is adjustablewith a control device 66. The braking mechanism 63 is adapted such thatthe friction between the braking head 64 and the arc-shaped outside ofthe nose-wheel holder 18 corresponds to preferably 80 percent or less ofsaid maximum torque. If this pre-set value is exceeded, the nose-wheelholder 18 will rotate.

In the embodiment in accordance with FIG. 9, a torque indicator 67, theconstruction of which is further illustrated by FIG. 10, is used insteadof a braking mechanism. A piston cylinder 68 flexibly connects the stand17 and the nose-wheel holder 18 and reacts to changes in the torque inthe nose-wheel holder 18. When 80 percent, for instance, of the maximumtorque is attained, the indicator 67 emits a signal to the driver, whothen has the opportunity of reducing the torque by changing thedirection of the traction vehicle. If this is not done and close to 100percent of the maximum torque is attained, a signal is emitted thatengages an alarm and automatically suspends the aircraft-movementoperation.

The engagement and hoisting device in accordance with the inventionenables the angle between the traction vehicle and the aircraft to bemeasured without direct contact. The risk of human error, that is thedanger of the driver or some other person assembling equipment of thetype described in SE-501 788, for instance, incorrectly is eliminated.

The traction vehicle in accordance with the invention enables simple andquick docking and coupling with the nose wheel or nose wheels withoutthe aircraft being disturbed from its parked position and without usinga screw joint or the like. The nose wheel has to be lifted only a shortdistance, for instance about 50-100 mm, to clear any unevenness in thetransport path. The height of the construction is sufficiently modest toallow it to clear the flaps hanging down on the sides of the nose-wheelstand. The engagement and hoisting device in accordance with theinvention with its said rotation girdle, formed by said journallingmembers 70, 71, is unique, in that it allows rotation and generation oftorque, respectively, during the application of tractive forces, as wellas braking forces, and in that the engagement elements acting againstthe nose wheel do not impede such a function in any way.

What is claimed is:
 1. A traction vehicle (2) for ground movement of anaircraft (1), having at least one nose wheel (4), which traction vehicle(2) comprises: a wheel-mounted chassis (7) and an engagement andhoisting device (12) that can be raised and lowered relative to thechassis (7) and is of a type that is brought into freely carryingengagement with the nose wheel (4) and which comprises a stand (17),being substantially U-shaped with its opening turned towards theaircraft (1), journalling members (15), flexibly connecting the stand(17) to the chassis (7), actuators (13), arranged between the stand (17)and the chassis (7) to raise and lower the engagement and hoistingdevice (12) relative to the chassis (7), and a nose-wheel holder (18),having an inner space (35) that can be opened in the direction of thenose wheel (4) for receiving the same, carrying members (43, 48) forcarrying the nose wheel (4) in said space (35), and forward and rearwheel supports (44, 49) for holding the nose wheel (4) in thelongitudinal direction of the traction vehicle, characterized in: thatthe nose-wheel holder (18) and the stand (17) are shaped as two separateunits and comprise co-operating journalling members (70, 71), arrangedin a circular arc and defining a vertical axis of rotation for saidunits (17, 18), and that the nose-wheel holder (18) is substantiallyU-shaped with its opening turned towards the aircraft (1) as viewed in astarting position, when the nose-wheel holder (18) is situated to bemoved into a position to receive the nose wheel (4).
 2. A tractionvehicle as claimed in claim 1, characterized in that the journallingmembers (70) of the stand (17) comprise a plurality of rolling elementsthat are mounted along a circular arc on a bottom plate (22) of thestand (17) by means of angle profiles (25), which rolling elementscomprise first and second rollers (26; 28), rotatably journalled to thehorizontal and vertical parts of each angle profile (25), respectively,to co-operate with the journalling members (71) of the nose-wheel holderin the form of vertical, opposing, concentric supporting and rollingsurfaces (39, 40) and a horizontal carrying and rolling surface (38),which supporting and rolling surfaces (39, 40) together with said firstrollers (26) define the vertical axis of rotation of the nose-wheelholder (18).
 3. A traction vehicle as claimed in claim 2, characterizedin that the nose-wheel holder (18) has outer edge portions (36) that arearc-shaped so that it acquires a vertical outside (37) with apre-determined radius that is somewhat greater than the radius of anarc-shaped inside (24) of the bottom plate (22) of the stand (17).
 4. Atraction vehicle as claimed in claim 1, characterized in that the stand(17) and the nose-wheel holder (18) are provided with co-operating stops(55, 56, 57) that are arranged to limit the rotation of the nose-wheelholder (18) in both directions from a central starting position.
 5. Atraction vehicle as claimed in claim 4, characterized in that the stand(17) is provided with two terminal position transducers (58, 59)arranged in front of the two stops (55, 56) on the stand (17) forsensing the stop (57) of the nose-wheel holder (18) to indicate theangle of rotation of the nose-wheel holder (18) relative to the stand(17) and the traction vehicle (2).
 6. A traction vehicle as claimed inclaim 1, characterized in that the nose-wheel holder (18) is arranged tobe able to rotate freely when the direction of travel of the tractionvehicle (2) changes relative to the aircraft (1).
 7. A traction vehicleas claimed in claim 1, characterized in that the engagement and hoistingdevice (12) comprises a rotation-inhibiting device acting between thestand (17) and the nose-wheel holder (18) for generating a moment oftorque between the stand (17) and the nose-wheel holder (18) when thedirection of travel of the traction vehicle (2) changes relative to theaircraft (1).
 8. A traction vehicle as claimed in claim 7, characterizedin that the rotation-inhibiting device consists of a break-device (60),arranged on the stand (17) and the nose-wheel holder (18) to secure thenose-wheel holder (18) against free rotation in a starting position, thebreak-device (60) being arranged to break when the nose-wheel holder(18) is subjected to a pre-determined, permitted torque relative to thestand (17).
 9. A traction vehicle as claimed in claim 7, characterizedin that the rotation-inhibiting device consists of a braking mechanism(62), arranged to act with a pre-determined braking power between thestand (17) and the nose-wheel holder (18), which braking power isarranged to be overcome when a pre-determined, permitted torque acts onthe nose-wheel holder (18).
 10. A traction vehicle as claimed in claim7, characterized in that the rotation-inhibiting device consists of atorque indicator (67), attached to the stand (17) and the nose-wheelholder (18) and arranged to sense and react to changes in the torque inthe nose-wheel holder (18).
 11. A device for a traction vehicle (2) forground movement of an aircraft (1), having at least one nose wheel (4),which traction vehicle has a wheel-mounted chassis (7), which device isdesigned to be brought into freely carrying engagement with and raisethe nose wheel (4) relative to the chassis and which comprises: a stand(17), being substantially U-shaped with its opening turned towards theaircraft (1), journalling members (15), flexibly connecting the stand(17) to the chassis (7), actuators (13), arranged between the stand (17)and the chassis (7) to raise and lower the engagement and hoistingdevice (12) relative to the chassis (7), and a nose-wheel holder (18),having an inner space (35) that can be opened in the direction of thenose wheel (4) for receiving the same, carrying members (43, 48) forcarrying the nose wheel (4) in said space (35), and forward and rearwheel supports (44, 49) for holding the nose wheel (4) in thelongitudinal direction of the traction vehicle, characterized in: thatthe nose-wheel holder (18) and the stand (17) are shaped as two separateunits and comprise co-operating journalling members (70, 71), arrangedin a circular arc and defining a vertical axis of rotation for saidunits (17, 18), and that the nose-wheel holder (18) is substantiallyU-shaped with its opening turned towards the aircraft (1) as viewed in astarting position, when the nose-wheel holder (18) is situated to bemoved into a position to receive the nose wheel (4).
 12. A device asclaimed in claim 11, characterized in that the journalling members (70)of the stand (17) comprise a plurality of rolling elements that aremounted along a circular arc on a bottom plate (22) of the stand (17) bymeans of angle profiles (25), which rolling elements comprise first andsecond rollers (26; 28), rotatably journalled to the horizontal andvertical parts of each angle profile (25), respectively, to co-operatewith the journalling members (71) of the nose-wheel holder in the formof vertical, opposing, concentric supporting and rolling surfaces (39,40) and a horizontal carrying and rolling surface (38), which supportingand rolling surfaces (39, 40) together with said first rollers (26)define the vertical axis of rotation of the nose-wheel holder (18). 13.A device as claimed in claim 12, characterized in that the nose-wheelholder (18) has outer edge portions (36) that are arc-shaped so that itacquires a vertical outside (37) with a pre-determined radius that issomewhat greater than the radius of an arc-shaped inside (24) of thebottom plate (22) of the stand (17).
 14. A device as claimed in claim11, characterized in that the stand (17) and the nose-wheel holder (18)are provided with co-operating stops (55, 56, 57) that are arranged tolimit the rotation of the nose-wheel holder (18) in both directions froma central starting position.
 15. A device as claimed in claim 14,characterized in that the stand (17) is provided with two terminalposition transducers (58, 59) arranged in front of the two stops (55,56) on the stand (17) to sense the stop (57) of the nose-wheel holder(18) to indicate the angle of rotation of the nose-wheel holder (18)relative to the stand (17) and the traction vehicle (2).
 16. A device asclaimed in claim 12, characterized in that the nose-wheel holder (18) isarranged to be able to rotate freely when the direction of travel of thetraction vehicle (2) changes relative to the aircraft (1).
 17. A deviceas claimed in claim 12, characterized in that the engagement andhoisting device (12) comprises a rotation-inhibiting device actingbetween the stand (17) and the nose-wheel holder (18) for generating amoment of torque between the stand (17) and the nose-wheel holder (18)when the direction of travel of the traction vehicle (2) changesrelative to the aircraft.
 18. A device as claimed in claim 17,characterized in that the rotation-inhibiting device consists of abreak-device (60), arranged on the stand (17) and the nose-wheel holder(18) to secure the nose-wheel holder (18) against free rotation in astarting position, the break-device (60) being arranged to break whenthe nose-wheel holder (18) is subjected to a pre-determined, permittedtorque relative to the stand (17).
 19. A device as claimed in claim 17,characterized in that the rotation-inhibiting device consists of abraking mechanism (62), arranged to act with a pre-determined brakingpower between the stand (17) and the nose-wheel holder (18), whichbraking power is arranged to be overcome when a pre-determined,permitted torque acts on the nose-wheel holder.
 20. A device as claimedin claim 17, characterized in that the rotation-inhibiting deviceconsists of a torque indicator (67), attached to the stand (17) and thenose-wheel holder (18) and arranged to sense and react to changes in thetorque in the nose-wheel holder (18).